1. Field of the Invention
This invention relates generally to ophthalmic solutions and methods for their use. More specifically, this invention relates to the reduction of corneal edema by the topical treatment thereof using ophthalmic solutions of specific composition.
2. Description of the Prior Art
Corneal edema often results from physical trauma or irritation and is also observed in association with diseases such as glaucoma. This condition results in blurred vision and can even lead to the essential loss of vision.
One common therapy approach to the management of corneal edema involves the use of topically applied hypertonic solutions. Many of the most effective prior art compositions utilize sodium chloride as the active ingredient. In order to be effective however, the sodium chloride concentration must be relatively high, on the order of 5%, a level which is about the maximum which can be tolerated by the normal human eye.
Experimental results obtained by treatment of human subjects with a variety of hypertonic agents are reported in an article by Luxenberg and Green, entitled "Reduction of Corneal Edema with Topical Hypertonic Agents", published in the American Journal of Ophthalmology, Vol. 71, No. 4, pp. 847-853 (1971). Those researchers investigated seven different hypertonic agents which listed in decreasing order of effectiveness are: 1. 5% sodium chloride ointment containing petrolatum and lanolin; 2. A buffered aqueous emulsion containing 5% sodium chloride and 5% glycerine; 3. a solution containing 5% sodium chloride with 5% gum cellulose and 2% glycerine; 4. a 30% sodium sulfacetamide solution in polyvinyl alcohol; 5. a 5% gum cellulose solution; 6. corn syrup containing sucrose, dextrose, and salt; and 7. a solution containing 0.9% methyl cellulose with 5% sodium chloride. As much as a 20% reduction in corneal thickness was observed with use of the 5% sodium chloride ointment. It was postulated that the ointment caused an osmotic withdrawal of fluid from the cornea thereby reducing its thickness and increasing its transparency.
Another article by Green and Downs entitled "Reduction of Corneal Thickness with Hypertonic Solutions" published in the American Journal of Ophthalmology, Vol. 75, No. 3, pp. 507-510, (1973), presented results obtained in experiments carried out with adult albino rabbits whose eyes had not previously been used experimentally. That work established the appropriateness of rabbits as experimental animals for this purpose and a comparison of the data presented in the two publications established that the effect of a hypertonic agent when applied to a human eye is approximately double that of the same agent when applied to a rabbit eye.
Ophthalmic solutions in general are well known and commonly used, particularly as contact lens wetting solutions. The solutions commonly comprise a mixture of one or more alkali metal salts, viscosity building agents, wetting agents and humectants, and medicaments of various kinds. Glycerine is a commonly used humectant but sorbitol and propylene glycol have also been suggested as humectants in ophthalmic solutions as is shown in U.S. Pat. No. 2,703,777. However, there is no recognition in the art that pentahydric and hexahydric alcohols such as sorbitol function to reduce corneal edema.